A multichannel spectrometer (also having a type with a non-crystal and without a PMT) comprising a scintillator, a PMT, an amplifier, and a multichannel spectrometer, is used for detecting gamma rays and identifying nuclide, wherein a typical operative processing is as follows: the scintillator absorbs (or partially absorbing) the gamma rays, the crystal emits light which is collected by the PMT which performs photoelectric conversion of the light thereon and linearly multiplies it as an electrical pulse; the amplifier performs a process of shaping and amplifying the electrical pulse; then the multichannel analyzer analyzes the amplified electrical pulse and converts it into a digital signal for subsequent processings. Since the above processing is a process of linear amplification and conversion, the multichannel spectrometer may be used for detecting a spectrum of the gamma rays. At present, various radiation detection systems using the multichannel spectrometer have been developed to determine the composition and type of the radiation based on the spectrum of the gamma rays detected by the detector.
The energy range of the gamma rays involved in the field of the radiation detection is generally from 0.03 to 3 MeV. Different energy regions of the gamma rays are generally corresponding to different application fields of radioactive sources, for example, the energy of the gamma rays from special nuclear materials concentrates in a relatively low energy region, the energy of the gamma rays from radioactive material for medical uses concentrates in a middle energy region, and the energy of the gamma rays from radioactive material for industrial uses concentrates in a relatively high energy region. Therefore, the radiation detection system not only requires highly sensitive radiation detecting capability, but also needs to detect gamma rays within the wide energy range involved in the radioactive material. The existing gamma ray spectrum detection systems directly measure precise information of a spectrum so as to acquire detailed information corresponding to the radiation, thus, the process of processing needs a relatively long time, whereas based on the consideration that different energy ranges of the rays are generally corresponding to different application fields of radioactive sources, if the energy range of the detected source and the category of the radioactive material can be fast distinguished at first so as to distinguish dangerous sources and daily used medical sources, then the workload of the front line officers can be greatly reduced, and the efficiency and accuracy of the radiation detection system can be improved.
The scintillator in the multichannel spectrometer may have many types, for instance, an inorganic scintillator (NaI, CsI, BGO) and an organic scintillator (organic crystal, organic liquid, organic plastic), etc., wherein a plastic scintillator, due to its characteristics of large volume, high detection efficiency, broad range of energy spectral response, moderate price, etc., is a commonly used detector in such fields as detection of special nuclear materials and other radioactive materials, low dose environmental measurement, gamma ray spectrum measurement. However, the energy resolution of the plastic scintillator is relatively poor, so generally it is not used for energy measurement of the gamma rays and nuclide identification. Some foreign manufacturers have combined a plastic scintillator detector with the multichannel spectrometer for distinguishing natural background and artificial radioactive sources and for eliminating a change in system sensitivity caused by fluctuation of the background.
If the purpose of the radiation detection system does not lie in precise determining of the radioactive material, but lies in fast determining the category of the radioactive material, then it is possible to use the plastic scintillator detector in the multichannel spectrometer so as to fast distinguish the category of the radioactive material by using the characteristics of the plastic scintillator. Thus, what is desired is to provide a radiation detection system using a multichannel spectrometer containing a plastic scintillator so as to fast determine the category of a radioactive material.